Method and apparatus for aligning tools provided on a C-frame

ABSTRACT

Tools (3, 4) mounted on the free ends of the arms of a C-frame applicator are aligned by providing the arms of the C-frame (1) in a form which is capable of flexing between a first position in which the axes of the tools (3, 4) are disposed at an angle relative to each other and a second position in which the axes of the tools are coaxial with each other. A workpiece (6) is arranged between the tools and a predetermined clamping load is applied to the workpiece (6) sufficient to flex the C-frame (1) from the first position towards the second position and bring the tools (3, 4) substantially into coaxial alignment. One or more of the tools (3, 4) is then actuated to apply a force to the workpiece (6).

BACKGROUND OF THE INVENTION

This invention relates to a method and an apparatus for aligning toolsprovided on a C-frame applicator.

C-frame applicators are used with suitable tools provided at the freeends of the C-frame which involve applying force at a point remote fromthe edge of a workpiece for the purpose of either fastening theworkpiece by such means as riveting, clinching or welding; or clamping,drilling, forming, or piercing the workpiece; or bringing othercomponents into engagement with the workpiece in an assembly operation.

In current practice, applicators for this purpose are normallyconstructed with C-frames which have sufficient rigidity to carry therequired load with minimal deflection. One major disadvantage of suchhigh rigidity C-frames is that they are inevitably heavy and bulky.C-frames could carry the same loads with far less weight and bulk ifgreater deflection under load was permissible This is a point of greatsignificance because heavy, bulky applicators cannot readily be carriedon prime movers such as economically sized robots.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a design which permitsgreater C-frame deflection whilst retaining the desired relativealignment of the tools over at least part of the operating cycle duringwhich a force is applied to a workpiece.

According to one aspect of the present invention there is provided amethod for aligning tools mounted on the free ends of the arms of aC-frame applicator comprising the steps of:

providing a C-frame the arms of which are capable of flexing between afirst position in which the axes of the tools are disposed at an anglerelative to each other and a second position in which the axes of thetools are coaxial with each other;

arranging a workpiece between the tool;

applying a predetermined clamping load to the workpiece to flex theC-frame from the first position towards the second position and bringthe tools substantially into coaxial alignment; and

thereafter actuating one or more the tools to apply a force to theworkpiece.

According to another aspect of the present invention there is providedapparatus for aligning tools mounted on the free ends of the arms of aC-frame applicator, wherein:

the arms of the C-frame are capable of flexing between a first positionin which the axes of the tools are disposed at an angle relative to eachother and a second position in which the axes of the tools are coaxialwith each other;

means is provided for applying a predetermined clamping load to theworkpiece to flex the C-frame from the first position towards the secondposition and bring the tools substantially into coaxial alignment; and

means is provided for actuating one or more of the tools to apply aforce to the workpiece.

The clamping load need not be sufficient to flex the arms of the C-framefully from the first position to the second position. Flexing to thesecond position can be accomplished with the aid of the force applied tothe workpiece by the tools. For example, in the case of riveting theforce applied to the workpiece by the tools may be such that the arms ofthe C-frame are flexed to the second position when the force exerted bythe tools is sufficient to cause the rivet to begin penetration of theworkpiece.

The predetermined clamping load may be constant, but it can beadvantageous if the clamping load is reduced from the predeterminedlevel as the force applied by the one or more tools to the workpiece isincreased. The result of the reduction in the clamping load is that thetotal applied load can be maintained substantially constant with theconsequence that the flexure of the C-frame remains substantiallyconstant.

Thus the present invention provides an applicator incorporating aC-frame which is capable of maintaining a desired relative alignment ofa first (upper) tool on one arm of the frame and a second (lower) toolon the other arm during at least part of the time when the tools areunder load.

In many fastening, forming or assembly operations, the most importantstage in terms of alignment is the workpiece entry stage, i.e. when therivet, drill or the like enters the workpiece. By ensuring that theworkpiece is clamped in a manner such that the tools are coaxial at theworkpiece entry stage, the present invention ensures accurate alignmentof the tools at least in the entry stage and, if desired, during theentire operating cycle.

Mounting the tools so that they come into alignment when the clampingforce is applied is beneficial even when there is no provision forreducing the clamping force. Having the tools in alignment afterclamping force is applied ensures, not only that there is correct toolalignment at the critical entry stage of the operating cycle, but alsothat any subsequent misalignment is limited to that generatedsubstantially by the operating load alone.

It may be desirable if the clamping load is not reduced below apredetermined minimum as the force applied by the one or more tools tothe workpiece is increased.

The initial clamping load may be less than the maximum force applied bythe one or more tools to the workpiece. Alternatively, the initialclamping load may be substantially the same as the maximum force appliedby the one or more tools to the workpiece.

For a better understanding of the present invention and to show moreclearly how it may be carried into effect reference will now be made, byway of example, to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a C-frame applicator in its free state with upper and lowertools out of alignment;

FIG. 2 shows the C-frame applicator of FIG. 1 under load with the toolsin coaxial alignment;

FIG. 3 is a cross-sectional view of one embodiment of an hydrauliccylinder for use with the applicator of FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

FIG. 1 shows an applicator comprising a C-frame 1 with an hydrauliccylinder 2, an upper tool 3 on one arm of the C-frame and a setting die4 on the other arm. The C-frame is mounted on a prime mover, such as arobot, by way of a compensator 5 to allow limited freedom of motion inone or more planes.

The C-frame can be constructed from a flexible carbon fibre material.The C-frame can be manufactured by outwardly flexing the arms of theframe prior to machining mounting blocks for the tools. If the arms areflexed over the distance they will flex under the predetermined clampingload, and the tool mounting blocks are then machined so that the toolsare in the correct coaxial alignment when mounted with the C-frame inits flexed configuration, the tools will adopt the desired coaxialalignment when the predetermined workpiece clamping load is applied.

The C-frame shown in FIG. 1 is in its free (unflexed) state and theupper tool and lower tool are therefore not in alignment.

FIG. 2 shows the applicator of FIG. 1 with the upper and lower toolsapplying a load to workpiece 6. The flexure of the C-frame is such thatthe upper and lower tools are in coaxial alignment.

When the upper and lower tools are mounted out of the desired alignmentand are brought into alignment by clamping and/or other pressure appliedto a workpiece, the point of workpiece contact moves relative to theC-frame. This is because the tools pivot as the arms of the C-frameflex, thus moving the point of workpiece contact towards and away fromthe base of the C-frame where the two arms are interconnected. If theworkpiece itself is not free to move, it is necessary to ensure that theC-frame is movable relative to the workpiece during the operating cyclebecause otherwise there would be a possibility of the tools skidding onthe workpiece surface as the arms of the C-frame flex with theconsequent risk, for example, that the workpiece surface could bedamaged. This can readily be achieved by mounting the C-frame on acompensator mechanism such as that described in International PatentPublication No. WO 94/02267.

FIG. 3 shows a sectional view of an hydraulic cylinder 2 with a piston 7and a clamping piston 8 operating in-line within a cylinder 2. A cavity10 is provided within the cylinder 2 intermediate the pistons 7 and 8,with a cavity 11 provided above the piston 7 and a cavity 18 providedbeneath the piston 8.

When cavity 11 is pressurised, piston 7 is subject to a downward forceequal to the area of the piston exposed to fluid in cavity 11 multipliedby the fluid pressure in cavity 11. It is also subject to an upwardforce equal to the area of the piston exposed to fluid in cavity 10multiplied by the fluid pressure in cavity 10. If, as is illustrated inFIG. 3, the area of piston 7 exposed to fluid in cavity 10 is equal tothe area of piston 8 exposed to the same fluid, then the upward force onpiston 7 is equal to the clamping load, and hence the net downward forceapplied by piston 7 to the tools at any point in time is equal to thearea of piston 7 exposed to cavity 11 multiplied by the pressure of thefluid in cavity 11 minus the clamping load.

If the fluid in cavity 10 is pressurised to provide a clamping loadequal to the load which is to be applied to the workpiece by the toolsand the pressure of the fluid in cavity 11 is raised to provide adownward force on piston 7 equal to the clamping load, piston 7 will bein equilibrium and the only load applied to the C-frame will be theclamping load. Reducing the fluid pressure in cavity 10 automaticallytransfers the load from the clamping mechanism to the tools without abringing the tools out of alignment because the flexing of the C-frameremains. unchanged.

If the fluid pressure in cavity 11 is raised to a level which provides adownwards force on piston 7 greater than the clamping load, piston 7will move downwards to apply an operating force to the workpiece equalto the force on piston 7 minus the clamping load. The excess load will,of course, flex the C-frame and thereby bring the tools out ofalignment, but the misalignment will be limited to that caused by theexcess load. Reducing the fluid pressure in cavity 10 againautomatically transfers the clamping load to the tools without causingany further tool misalignment.

Control of the fluid pressure in the cavities 10, 11 and 18 can beeffected by means of directional valves 14 and 21.

Directional valve 14 can be moved to a first position to connect a pumpline 12 to a cavity 10 in cylinder 2 intermediate the pistons 7 and 8 byway of a pilot operated check valve 15. In this configuration piston 7,which operates a main plunger 20, is forced upwardly as shown in FIG. 3,and piston 8, which operates a clamping mechanism, is forced downwardlyto bring the clamping mechanism into contact with a workpiece 6 and toapply a predetermined clamping force. As piston 7 rises, the hydraulicfluid in a cavity 11 above the piston 7, as shown in FIG. 3, isdischarged directly to a tank 13 (illustrated diagrammatically in FIG.3). As piston 8 descends, the hydraulic fluid in a cavity 18 beneathpiston 8 is discharged directly to tank 13.

Directional valve 14 can be moved to a second position to connect cavity18 directly to the tank 13 and to connect cavity 10 to the tank 13through a programmable pressure relief valve 17. In this configuration,the hydraulic pressure in cavity 10 is controlled by programmable reliefvalve 17.

Directional valve 21 can be moved to a first position to connect pumpline 12 to cavity 11. When the fluid pressure in cavity 11 rises to thepoint where the downward force on piston 7 is greater than the upwardforce on piston 7 from the fluid in cavity 10, piston 7 will movedownwards discharging fluid from cavity 10 through programmable pressurerelief valve 17. When a tool connected to plunger 20 contacts theworkpiece 6 it will apply a pressure to the workpiece equal to thedownward force on piston 7 minus the upward force on piston 7. If nowthe settings of programmable pressure relief valve 17 are reduced, thefluid pressure in cavity 10 will drop thereby reducing the clampingforce on the workpiece 6 and increasing the operating force applied bythe tooling. When the fluid pressure in cavity 11, as measured by apressure switch 22, and the fluid pressure in cavity 10, as measured bya pressure switch 23, have reached the desired levels, directional valve21 can be moved to a second position connecting cavity 11 to tank 13 anddirectional valve 14 can be moved to a third position connecting cavity18 to pump line 12 and connecting cavity 10 to the tank 13 via pilotoperated check valve 15. In this configuration, piston 8 and piston 7will rise thereby retracting the clamping mechanism and the tools fromthe workpiece 6.

What is claimed is:
 1. A method for aligning tools (3, 4) mounted onfree ends of the arms of a C-frame applicator comprising the stepsof:providing a C-frame (1) having arms which are capable of flexingbetween a first position in which axes of tools (3, 4) mounted thereonare angularly inclined relative to each other with their axesintersecting, and a second position in which the axes of the tools arecoaxial with each other, at least one of the mounted tools being capableof actuation to apply force; arranging a workpiece (6) between themounted tools; applying by means of the arms a predetermined clampingload to the workpiece (6) to flex the C-frame (1) from the firstposition towards the second position and bring the tools (3, 4)substantially into coaxial alignment; and after applying thepredetermined clamping load, actuating the at least one tool (3, 4) toapply a force to the workpiece (6).
 2. A method according to claim 1,wherein the predetermined clamping load is substantially constant.
 3. Amethod according to claim 1, wherein the clamping load is reduced fromthe predetermined level as the force applied by the at least one tool(3, 4) to the workpiece (6) is increased.
 4. A method according to claim3, wherein the clamping load is not reduced below a predeterminedminimum as the force applied by the at least one tool (3, 4) to theworkpiece (6) is increased.
 5. A method according to claim 1, wherein aclamping load prior to actuation of the at least one tool is less than amaximum force applied by the at least one tool (3, 4) to the workpiece(6).
 6. A method according to claim 1, wherein a clamping load prior toactuation of the at least one tool is substantially the same as amaximum force applied by the at least one tool (3, 4) to the workpiece(6).
 7. A C-frame applicator incorporating apparatus for aligning tools(3, 4) mounted on free ends of arms thereto, at least at one of themounted tools being capable of actuation to apply force, wherein:thearms of the C-frame (1) are capable of flexing between a first positionin which axes of the mounted tools are angularly inclined relative toeach other with their axes intersecting, and a second position in whichthe axes of the mounted tools are coaxial with each other; means (2) isprovided on the arms for applying a predetermined clamping load to theworkpiece (6) to flex the C-frame (1) from the first position towardsthe second position and bring the tools (3, 4) substantially intocoaxial alignment; and means (2) is provided for actuating at least oneof the tools (3, 4) to apply a force to the workpiece (6).
 8. A C-frameapplicator as claimed in claim 7, wherein the predetermined clampingload is substantially constant.
 9. A C-frame applicator as claimed inclaim 7, wherein the clamping load is reduced from the predeterminedlevel as the force applied by the at least one tool (3, 4) to theworkpiece (6) is increased.
 10. A C-frame applicator as claimed in claim9, wherein the clamping load is not reduced below a predeterminedminimum as the force applied by the at least one tool (3, 4) to thework-piece (6) is increased.
 11. A C-frame applicator as claimed inclaim 7, wherein a clamping load prior to actuation of the at least onetool is less than a maximum force applied by the at least one tool (3,4) to the workpiece (6).
 12. A C-frame applicator as claimed in claim 7,wherein a clamping load prior to actuation of the at least one tool issubstantially the same as a maximum force applied by the at least onetool (3, 4) to the workpiece (6).